Date: Sat, 27 Mar 1999 09:04:43 -0700
From: "Bruce C. Anderson" 
Subject: Fuel/Oil Ratios

Howdy Gary

        I have an 86 TY350 that I have owned since 89, and have used Belray
synthetic at 70/1 for almost the entire time, with no apparent ill effects.
I would have used 100/1, except that I just didn't have the courage. 

        According to what I have heard the best ratio for POWER is some
where between 26/1 to 33/1.  For Trials, this may not be an optimum fuel/oil
ratio, because at lower engine speeds, oil tends to condense, and collect in
the crankcase, then when high throttle settings are used, this excess oil
may cause the engine to run poorly until it is burned out.  This may be why
you used to see World riders revs their engines up high when at a dead stop
in front of an obstacle that they could not afford the engine to hesitate
on.  Oh yea, one other thing, the engine tends to run hotter at these ratios.

        Unless you are a world class rider, or riding at high altitude, you
don't necessarily need more power out of a TY350, so using the best power
fuel/oil ratio may not be worth the possibility of oil fouling the engine
after prolonged low speed operations.

          I have had good luck 70/1 fuel/oil ratio, no oil pooling problems,
no apparent wear problems, and no seizing.  I change plugs once a season
whether it needs it or not.   (BOSCH PLATINUM!!!!  The ONLY two stroke spark
plug)

        If you are not familiar with what happens to jetting when you change
fuel/oil ratios, here is a short primer:

        Any time that you change fuel/oil ratios it affects the amount of
fuel that goes through the jets.  A 28/1 fuel/oil ratio, may seem rich,
since it has so much oil in it, actually, it is a LEAN ratio.  A 70/1
fuel/oil ratio seems to be a lean ratio because it has so little oil, 70/1
is a RICH ratio.  At 28/1, 28 units of gasoline pass through the jets for 1
unit of oil, at 70/1, 70 units of gasoline pass through the jets for 1 unit
of oil. 

        Rich, and Lean, are terms that apply to the of gasoline/air ratio
that is available for combustion, not the amount of lubricating oil in the
mixture.  So if you change from a lower to a higher fuel/oil ratio, say from
a 28/1 to a 70/1, then you may need to lean your jetting.  This may include
adjusting low speed air, change to a leaner low speed jets, change sliders,
needle position, needle/needle jet sizes, and use a leaner main jet.

        If you go from 70/1 to 28/1 fuel/oil ratios you might have to
enrichen your jetting.

I have made some modifications to the stock carburetor that seem to work
fine at a 70/1 fuel/oil ratio, and would be glad to share them with you if
you'd like.

DISCLAIMER

        The above is only my opinion, and I couldn't buy a clue if I went to
the clue store with a coupon and my momma.

Good Luck
Bruce
Prescott Valley AZ. USA.